The invention relates to an arrangement for focusing the image of an object onto an image plane, wherein the image is derived from an objective lens system, adapted to be adjusted by a setting device which changes the distance of the objective, or a portion thereof, with respect to the image plane.
The magazine "Popular Photography", Vol. 78, No. 1, 1976, page 94 left-hand column, line 24 to the next to last line, it is generally indicated that it is possible to provide an image detector, which is supplemented by an electrical circuit, to form a contrast measuring device which may be employed to set the range of a photographic camera relative to an object. The image detector is to contain a plurality of individual photo-cells, the electrical signals of which are scanned sequentially. The contrast measuring device could be further utilized to produce an adjusting signal which would influence the focal distance setting of the camera objective lens system.
The object of the invention is to provide a practical solution, which can be achieved in a simple manner, to the problem of automatically controlling an objective lens system to effect the focusing of the image of an object in an image plane. Proceeding from an arrangement, such as above referred to, this is achieved in the present invention by disposing a CTD (Charge-transfer-device) image sensor in the image plane, which sensor possesses a number of image points aligned to a part of the image, and in which the output of the CTD image sensor, provided for the sequential read-out of the image points, is connected to an evaluating circuit which, for a sequence of discrete values lying within a given range, forms in each case read-out signals which correspond to the mutual contrast of the read-out image points, with such read-out signals being integrated in the evaluating circuit. The latter may be provided with an output at which an adjusting signal is supplied which may be utilized to adjust the objective lens system to the distance assigned to the integrated read-out signal having the greatest magnitude, or may be utilized to indicate the distance of the object.
The advantage achieved in the present invention, in particular, resides in the fact that the CTD image sensor can be monolithically integrated together with the individual components of the evaluating circuit on a semiconductor substrate, to form a semiconductor module which effects the focusing and which can be easily accommodated in various devices which employ focusing, without materially or even noticeably increasing the space requirement.